A. Ismail

Fermi level pinning by interface states: A calculation of the height and the shape of the Schottky barrier

Abstract A calculation of the potential distribution of the space charge region of a metal-semiconductor contact is proposed, which is based on the theories of Schottky and Bardeen. Inspired by the defect model of Spicer et al. , we assume that interface states are spread over several atomic layers inside the semiconductor. Thus the “neutral level” of Bardeen can be reached at the most buried states. Particular attention is paid to conditions for which such Fermi level pinning is possible.

Formation and properties of (Au, Al, Ag, In) (InP-GaAs) Schottky diodes; contribution of the semiconductor surface to the diode characteristics

Abstract The interaction of Au, Ag, Al, In with etched or cleaved surfaces and with surfaces pertubed by oxygen exposure or by the deposition of a thin metal interlayer is studied. By using work function and surface photovoltage topographies, interface formation and Fermi-level pinning is studied. The contribution of both the initial surface properties and the nature of the metal to the features of the interfaces and of the diodes is analysed.

A study of the cleaved InP surface by CPD and SPV topographies

Abstract We study the electronic properties of cleaved InP surfaces by work function and surface photovoltage topographies. The results show that the Fermi level can be pinned at about 1 eV above VBM by acceptor and donor surfaces states induced by cleavage defects. We suggest a two-state model and give some indications for possible density and energy of these states. Then we study the surface properties after submonolayer Ag coverage and discuss the pinning conditions.

Problems relevant to the use of optical pyrometers for substrate temperature measurements and controls in molecular beam epitaxy

In molecular beam epitaxy an optical pyrometer is frequently used to determine substrate and epilayer temperatures during the growth of semiconductors. This implies a calibration of the pyrometer and a correct analysis of its indications. In this article we discuss problems presented by this calibration. We first compare the temperatures measured on the sample holder and on several substrates (GaAs, InAs, GaSb) attached to it. Then we present examples of temperature variations recorded during the growth of AlSb and GaSb on GaSb or GaAs substrates. GaSb epilayers thicker than 0.1 μm induce a 40°–60° decrease of the measured temperature. AlSb deposition on GaSb produces temperature oscillations. We discuss these variations in terms of apparent and true temperature variations.

Properties of the contact on ion cleaned n and p type silicon surfaces

Abstract Schottky contacts were produced by silver evaporation on Si(100) surfaces cleaned by ion sputtering and partial annealing. The samples work function were measured before and after metal deposition with the Kelvin method, in an experimental set-up which allowed a topografical study and direct comparison between n and p types. Clean surfaces with and without a residual layer of oxide was achieved and controlled by AES. It was found that the Fermi level of all the surfaces was pinned by donor states created by the bombardment and that there was no barrier on n type and an important surface barrier on p type. The diodes we obtained presented no barrier on n type and a rectifying contact on p type. So we deduced that the Schottky barrier is already fully formed before metal contact is achieved. Furthermore study of the electrical properties of the diodes had shown that the bombardment creates donor states responsible for the barrier and a perturbated layer with deep acceptor traps responsible for the current flow mechanism. A residual layer of oxide and a post annealing of the device did not noticeably change the Schottky barrier in the diodes achieved on p type but led to clearly differenciated performances for the diodes achieved on both p and n type substrate. So we therefore concluded that the characteristics of the deep acceptor traps of the superfacial layer are modified by the oxide and annealing, both of which on the other hand having no effect on the surface donor states.

Silver Schottky diodes on Kelvin, AES and LEED characterized (100)surfaces of GaAs cleaned by ion bombardment

Abstract Schottky contacts were produced by silver evaporation on GaAs surfaces cleaned by ion bombardment. The samples work function were measured before and after metal deposition with the Kelvin method in an experimental set up which allowed a topographical study and direct comparison between n and p types. Surfaces were controlled by AES and LEED. It was found that the Fermi level of all the surfaces was pinned in the midgap range and so there was, on both n and p types, an important surface barrier qVs whose value did not strongly depend on the surface preparations we used. The diodes we obtained also presented an important barrier φB for both n and p types. So it was deduced that diode barriers corresponded to those that were created by surface states and that metal deposition did not noticeably modify these states. On the other hand, surface preparations played an important role in the electrical performances of the diodes. It was deduced then that ion bombardment deteriorated the first atomic layers of the semiconductor.

The interaction of Ag, In and Al overlayers with InP (110): surface and diode studies of the effect of indium interlayers

Abstract In this paper, we study the modification of the electronic properties of cleaved InP surfaces induced by Ag, Al and In depositions and the effect of indium interlayers on the diode properties. We show that the surface of the interface behaviour can influence the position of the Fermi-level pinning. Possible state density modifications and In compensation are discussed in terms of the defect model, and the results are explained using a cluster formation model.

Chemical etching and annealing induced GaAs(100) surface properties

Abstract We Study chemically cleaned or annealed GaAs(100) surfaces by using AES, work function (TCPD) and surface photovoltage topographies (TSPV). We show that whatever the etch, the Fermi level is pinned: acceptor and donor states are needed to explain these results which are analysed by comparing the models of Grant and of Spicer. However, some different properties are related to the surface preparation and treatment: electronic affinity or surface barrier height modifications, work function uniformities, surface composition, etc.

A study of oxygen interaction with GaSb cleaved surfaces by work function and photovoltage measurements

This paper deals with oxygen sorption at room temperature on cleaved GaSb surfaces. The mechanism was studied in the range 10-1-10-4 langmuirs by measuring contact potential differences in the dark and under illumination on well-cleaved and poorly cleaved n- and p-type GaSb, with an ionization gauge either on or off. After a study of the first steps of oxygen sorption and of the Fermi level pinning on n- and p-type GaSb, the results are compared with those of the Spicer-Lindau group and are explained by a model with two surface states, one acceptor state of density Na and one donor state of density Nd, with the ratio Na/Nd varying during the exposure to oxygen.

The interaction of Ag and Al overlayers with InP (110): Surface and diode studies of the effect of Sb interlayers

We study the properties of the Sb–InP (110) interface by contact potential difference, surface photovoltage, and Auger electron spectroscopy, and then the effect of the Sb interlayer on Al and Ag–InP (110) Schottky diode properties. For Sb coverage <1 ML, the surface Fermi level EFs is strongly pinned near the conduction band and the electron affinity decreases. The Sb interlayer effect on the Schottky contacts Al–InP and Ag–InP is already noticeable for a submonolayer of Sb. The EFs position moves to a common position situated at about 1 eV above the valence band maximum and the abruptness of the interface is changed. The interaction of the metal with the semiconductor is partially or completely screened. In the case of Al–InP contact In or P diffusion into the metal is stopped. The interface is more abrupt in Al–InP contact, less abrupt in Ag–InP contacts. This is due to a high density of interface states in the gap, the origin of which could be found in a possible modification of the surface relaxation...